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Errors, Type I and Type II

  1. Gregory R. Hancock

Published Online: 30 JAN 2010

DOI: 10.1002/9780470479216.corpsy0319

Corsini Encyclopedia of Psychology

Corsini Encyclopedia of Psychology

How to Cite

Hancock, G. R. 2010. Errors, Type I and Type II. Corsini Encyclopedia of Psychology. 1–2.

Author Information

  1. University of Maryland, College Park

Publication History

  1. Published Online: 30 JAN 2010


The goal of most social science research is to infer whether variables relate to each other in one or more populations of interest. Statistical tests are a tool used to assist in this inferential process by evaluating data from samples drawn from the population(s) of interest; these statistical tests are, however, by no means foolproof. Occasionally sample information would seem to imply that, for example, variable X is related to variable Y in the population, when in fact no such population relation exists. Such an inaccurate inference is termed a Type I Error (or “alpha error”). On the other hand, sample data may seem to imply that X and Y appear unrelated, when indeed those variables do have a relation in the population. This inaccurate inference is termed a Type II Error (or “beta error”). These two types of errors are discussed in the context of an illustrative research example.